A stiffener device has been used with lead frames for die assembly and package production to provide support for flexible, and even flimsy, substrates. The stiffener can assist in preventing or reducing damage to the substrate and associated electrical components. Stiffeners are typically attached to lead frames by applying a strip of adhesive tape or a layer of adhesive paste to the stiffener and/or the surface of the lead frame.
Referring to FIG. 1, a prior art semiconductor die package 2 disposed within a package mold 4 is shown. Package 2 typically comprises a lead frame 6 (or other substrate), adhesive element 8, one or more dies 10, adhesive element 12, a metal or plastic stiffener 14, and an encapsulating material 16. Package mold 4 comprises mold plates 18. Mold plates 18, as illustrated in FIG. 1, define a mold gate 20 and a cavity 22 disposed within package mold 4.
The package illustrated in FIG. 1 can be assembled by first constructing a die assembly 24. Die assembly 24 comprises one or more dies 10 secured to lead frame 6 with adhesive element 8. After die assembly 24 is assembled, plastic or metal stiffener 14 is secured to lead frame 6 of die assembly 24 with adhesive element 12, and the die assembly is placed between mold plates 18 within cavity 22. Encapsulating material 16 is then introduced into package mold 4, through mold gate 20, and flows over die assembly 24. In such instances, encapsulating material 16 is generally heated prior to being injected into package mold 4, and flowed in and around die assembly 24, covering all or a portion of lead frame 6 and/or dies 10. Thereafter, encapsulating material 16 is allowed to harden. Mold plates 18 can then be removed whereby package 2, as illustrated in FIG. 2, remains.
In some situations, the stiffener comprises a metal or metal alloy. Unfortunately, metal stiffeners are difficult to cut with conventional, diamond-tipped saws. As such, metal stiffeners are burdensome to segment before and during package production. Likewise, the produced packages that incorporate metal stiffeners are also difficult to cut. As a result, it is laborious to separate packages from one another. Additionally, metal stiffeners are expensive and therefore contribute to added expense of the package.
Plastic stiffeners have also been used to support a lead frame. Typically, in those cases where a plastic stiffener is used, a thermoplastic or thermosetting polymeric material is heated and introduced into a mold and, upon cooling, the mold is opened and a plastic stiffener is produced. Thereafter, the plastic stiffener is secured to the lead frame using an adhesive tape or paste.
Plastic stiffeners offer several advantages over metal stiffeners. For one, plastic stiffeners can be more easily cut. This allows the plastic stiffeners to be segmented and packages separated from one another. Also, plastic stiffeners are less expensive than metal stiffeners. As such, the cost of semiconductor processing can be reduced. However, plastic stiffeners, like their metal counterparts, have associated disadvantages.
For example, a supply of adhesive must be procured in order to attach the stiffeners to lead frames. Purchasing, inventorying, and storing the adhesive can add to the cost of die assembly and package processing. Further, attaching a stiffener requires an attachment step be performed during processing, which can require additional processing apparatus, add to processing time, and provide an opportunity for error. Therefore, an improved stiffener and method of applying the same to a substrate is desirable.